Continental Extension in the western Woodlark Basin: P-T-t-D constraints from Normanby and Misima Islands

巴布亚新几内亚东南部的伍德拉克盆地是世界上扩展最快的裂谷之一，为研究大陆岩石圈在从裂谷到海底扩张的过渡过程中如何破裂提供了一个天然实验室。正是在这里，首次发现了D'Entrecasteaux群岛的活跃变质核杂岩（例如，Hill et al.,1992）。这些岛屿保存着一些地球上已知的最年轻、最迅速发掘的变质岩和火成岩（Baldwin et al.,1993）。恩特卡斯多岛变质核杂岩下部板块的发掘，提供了与伍德拉克盆地-海底扩张体系向西扩张同步的活跃大陆伸展和岩浆活动记录。虽然已经了解了Moresby海山（Taylor and Huchon, in review）附近的海底扩张历史（如Taylor et al.,1999）和从裂谷到扩张的转变，但要全面了解Woodlark盆地大陆裂谷的历史和机制，还需要更多的陆上地质研究。大陆岩石圈的破裂提供了事件的热记录，这些记录以同位素变化的形式保存在矿物中。这些事件可以用热年代学来揭示，当与P-T-D约束相结合时，可以用来确定与大陆伸展和岩浆作用有关的发掘时间和速率。为了进一步研究Woodlark盆地西部大陆裂谷和海底扩张之间的关系，PI计划：1)记录位于活跃裂谷尖端以西的D' entrecastoaux群岛最东端的Normanby岛上暴露的岩石的P-T-t-D历史；2)记录Misima岛上暴露的岩石的P-T-t-D历史；3)确定D' entrecastoaux群岛岩心杂岩下部板块榴辉岩相变质作用的时代。结果将与以前在D' entrecastaux群岛和Moresby海山进行的P-T-t-D研究进行比较。大陆伸展和岩浆活动时间的纵向和纬度变化（或缺乏）将与伍德拉克盆地海底扩张的历史和最近提出的该地区演化模型相联系来解释。

The Woodlark Basin of southeastern Papua New Guinea is one of the world's most rapidly extending rifts and provides a natural laboratory to study how continental lithosphere ruptures during the transition from rifting to seafloor spreading. It is here that the active metamorphic core complexes of the D'Entrecasteaux Islands were first discovered (e.g.,Hill et al.,1992). These islands preserve some of the youngest, most rapidly exhumed metamorphic and igneous rocks known on Earth (Baldwin et al.,1993).The exhumed lower plates of the D'Entrecasteaux Island metamorphic core complexes provide a record of active continental extension and magmatism synchronous with the westward propagation of the Woodlark Basinseafloor spreading system. While the seafloor spreading history (e.g.,Taylor et al.,1999) and the transition from rifting to spreading in the vicinity of the Moresby Seamount (Taylor and Huchon, in review) is known, more onshore geologic research is required to fully understand the history and mechanisms of continental rifting in the Woodlark Basin. Rupturing of continental lithosphere imparts a thermal record of events that are preserved as isotopic variations within minerals. These events can be revealed using thermochronology, and when integrated with P-T-D constraints, can be used to determine the timing and rates of exhumation associated with continental extension and magmatism. The PI's propose to further investigate the relationship between continental rifting and seafloor spreading in the western Woodlark Basin by 1) documenting the P-T-t-D histories of rocks exposed on Normanby Island, the easternmost of the D'Entrecasteaux Islands, located west of the active rift tip, 2) documenting the P-T-t-D histories of rocks exposed on Misima Island, part of the southern rifted continental margin and 3) determining the age of eclogite facies metamorphism in the exhumed lower plates of the D'Entrecasteaux Islands core complexes. Results will be compared to previous P-T-t-D studies on the D'Entrecasteaux Islands and Moresby Seamount. Longitudinal and latitudinal variations (or lack thereof) in the timing of continental extension and magmatism will be interpreted in relation to the history of seafloor spreading in the Woodlark Basin and recently proposed models for the evolution of the region.